1. Field of the Invention
This invention relates to a method of reading out a radiation image of one or more spots stored and recorded on a stimulable phosphor sheet. Particularly, the invention relates to a radiation image-reading method which is advantageously employed for reading out a radiation image of one or more colonies in the form of spot stored and recorded on a stimulable phosphor sheet which is utilized in autoradiography for hybridization of DNA colonies.
2. Description of Prior Art
There has been heretofore known use of a stimulable phosphor sheet as a radiation-sensitive material in the autoradiography for hybridization of DNA colonies.
In the case of screening genes utilizing the autoradiography such as the the case of screening fragments of DNA having a number of base sequences (e.g., human DNA) by a colony hybridization, very troublesome operations are required. For example, in order to find out the desired colony or colonies (one to several colonies) from a great number of colonies such as 10.sup.6 colonies, the 10.sup.6 colonies are divided into 10.sup.3 groups of colonies to give 10.sup.3 filters carrying each group, and each of those filters is to be examined to detect the location of the desired colonies having a radioactively labeled substance. In other words, in order to find out the desired few colonies from a great number of colonies such as 10.sup.6 colonies, it is required to detect a filter on which the desired colony or colonies are carried and further to locate positions of the colonies on the filter by examining all of the 10.sup.3 filters.
In the above-mentioned autoradiography, each position of one or more colonies can be detected using stimulable phosphor sheets (i.e., radiation image storage panels, serving as radiation sensitive material). The radiation sensitive material is used in autoradiography for copying thereon the colony containing a radioactively labeled substance to obtain locational information of the colony on the filter.
The locational information of the colony on the filter can be detected by reading out a radiation image of one or more spots corresponding to the position of the radioactively labeled substance on a stimulable phosphor sheet.
The stimulable phosphor sheet is a sheet comprising a stimulable phosphor which absorbs (stores) a portion of radiation energy when exposed to a radiation and emits a light (stimulated emission) corresponding to the stored energy upon excitation with stimulating rays such as visible light. The stimulable phosphor sheet per se is already known.
For reading out the desired information of the radiation image stored and recorded on the stimulable phosphor sheet, there has been previously proposed or put into practical use a method of irradiating the surface of the stimulable phosphor sheet with stimulating rays to perform raster scanning or plane spiral scanning with a spot of convergent stimulating rays condensed into a point and detecting the stimulated emission produced under the irradiation, by means of a photodetector. In this method, it is required to scan the whole surface of the stimulable phosphor sheet with the stimulating rays, so that a long period of time is needed for reading one phosphor sheet. For one screening process of DNA, the above-mentioned reading operation should be done with respect to all of the 10.sup.3 filters, and hence an extremely long period of time is needed for one DNA screening. In the above-mentioned case, for instance, the proportion of the colonies to be found out to all of the colonies in one DNA screening process is very small, namely, a proportion of only one to several colonies to 10.sup.6 colonies, and therefore the desired (aimed) colony does not exist in most of the filters. Accordingly, it is unfavorable to spend such a long period of time for detecting the filters where aimded colonies may exist at such small proportion, and hence it is desired to make the time for reading the radiation image as short as possible and to efficiently perform one screening operation in a short period of time.
Further, it is unfavorable to store a master plate having colonies therein for a long time, because the colonies are not always stable. From this viewpoint, the time for reading the radiation image is required to be shortened.
Furthermore, the genetic screening has been widely carried out with the development of biotechnology, and the procedure of reading out radiation image of one or more spots on a stimulable phosphor sheet is more frequently utilized in the autoradiography, so that the apparatus for reading out the radiation image employed in the autoradiography is desired to be minimized, simplified and obtainable at a low cost.